1. Field of the Invention
The present invention relates generally to honeycomb manufacturing apparatus and more particularly to a mechanical apparatus for expanding a stack of stagger-bonded ribbon to create a sheet or panel of honeycomb.
2. Brief Description of the Prior Art
The term "honeycomb" is often used to describe an open-celled structure similar to a bee's honeycomb. This term, however, is not generally limited to a structure made of hexagonally shaped and interconnected open cells and usually extends to include a structure made of other shapes of interconnected cells as well. For example, such cells could be square, rectangular or six-sided, and are not limited to the hexagonal configuration. Accordingly, it is this extended meaning that will be attached to the term "honeycomb" as used in this specification.
Typically, a panel of honeycomb is made by first placing rectangular sheets of material on top of one another to form a stack. As an individual sheet is placed it is bonded to the sheet below it by means of parallel, equally spaced-apart lines of bonding which extend across the entire surface of the sheet. The lines of bonding of every subsequent sheet are formed directly above the spaces between the lines of bonding of each previous sheet. This process is known as stagger-bonding.
Once a stack of sheets has been formed it is sliced, in direction perpendicular to the direction of the lines of bonding, into narrow strips to form a stack of stagger-bonded ribbons. These strip stacks are then expanded in a direction transverse to the planes of the individual ribbons, to form the panel of honeycomb.
One recent implementation of this technique has been to expand stagger-bonded ribbons of flexible material to form the cores for resilient honeycomb pads and the like. (See, for example U.S. Pat. No. 5,039,567). The expansion has typically been achieved by hand with a technician hooking each side of the material to be expanded over pins arrayed along the side of a stretcher plate. Such manual technique is both inefficient and expensive.
Another problem with manual honeycomb expansion methods is that, from a practical standpoint, only elastic or pliable materials are suitable for being expanded by hand. As a consequence, stiff or brittle materials are not usually made into honeycomb using the stagger-bonded ribbon technique as there has heretofore been no convenient way to expand the rigid and sometimes fragile bonded ribbons into open-celled sheets. However, many such materials are desirable for some types of honeycomb applications because of their strength-to-weight ratio. Since some of these desirable materials become pliable when exposed to heat, it would be advantageous to have means available which could simultaneously heat the ribbons and expand or stretch them into the open-celled honeycomb configuration.
Historically, honeycomb expanders have been used in conjunction with food-packaging machinery. For example, U.S. Pat. Nos. 4,435,941, 4,250,684 and 4,584,821 disclose machinery for packaging fruit into expanded honeycomb-filled containers. Such apparatus typically uses suction to engage the outer ribbons to effect the expansion operation and hold the honeycomb open until fruit is inserted. While appropriate for some applications, the use of vacuum mechanisms of this type would be unnecessarily complex and, in some cases unworkable and expensive, method of expanding honeycomb. For example, whereas the honeycomb dividers used for food packing are large in size and have large cell structure making the use of vacuum apparatus practical, honeycomb materials used in many other applications often have quite small cell structures. To use suction as a means of engagement in an expander for small-celled honeycomb would be very difficult because, among other things, of the need to vary the pitch of the suction points during the expansion process.